An image projector apparatus such as a microfilm strip reader or reader/printer apparatus or a video projection television receiver uses a viewing screen of the transmission type through which an image projected onto the viewing screen is to be viewed by a viewer situated in front of the screen. A prior-art transmission viewing screen however has a problem in that the beam of light transmitted through the viewing screen is caused to diffuse in various directions from the screen and diverges outwardly from the field of view. The image to be viewed through the viewing screen thus tends to be blurred toward the edges of the viewing screen and has marginal areas which could not be viewed clearly from the viewer.
For the purpose of overcoming such a problem inherent in a prior-art transmission viewing screen, a transmission viewing screen for an image projector apparatus is proposed which is provided with light converging means for the screen. The light converging means is implemented by a Fresnel lens attached to or formed on the inner surface of the viewing screen so that the beam of light transmitted through the viewing screen is caused to converge past the screen to form brighter and clearer image areas along the edges of the screen. A transmission viewing screen of this nature however has a drawback in that the successive steps in the Fresnel lens form stripes or fringes in the image frame to be viewed through the transmission viewing screen and impairs the quality of the image, particularly, the resolution of the image.
The present invention contemplates elimination of these drawbacks of known transmission viewing screens for image projector apparatus and, accordingly, it is an important object of the present invention to provide an improved transmission viewing screen capable of producing an image having clear and bright marginal areas and an excellent resolution.